Circuit and method for measuring the amplification factor of an in-circuit or out-of-circuit transistor

ABSTRACT

A method and a circuit for measuring the amplification factor (beta) of an in-circuit transistor is disclosed. A first potential of one polarity is applied across a first fixed resistor and the collector-emitter path of the transistor. A second potential of opposite polarity is applied across a first variable resistor and the first fixed resistor, the resistance of the first variable resistor being adjusted until the net voltage across the first fixed resistor is zero. The first potential is also applied through a second fixed resistor, a second variable resistor, and the base-emitter path of the transistor, and the second variable resistor is adjusted until a predetermined current flows through the first fixed resistor and the collectoremitter path of the transistor. A meter is provided for measuring the current through the first and second fixed resistors and obtaining their ratio.

' [73] Assignee [72] Inventor Timl NX.

[21 Appl. No. 705,356 221 Filed Feb. 14, 1968 [45"] Patented JulyZO, 1971- RCACorporation 154 'c'urculr summit Mn'sunuc 111a mruncmon rm'on or an lN-CIRCUIT 0R QUT-OF CIRCUI'I'TRANSISTOR 1QClalrn|,4Drawlng'Il|i.' v 52 user I :4z4/1ss'r 51 1| :.c|......-... coon/22 r501 'FieldolSeoreh x... 324/l58, V --,1ss1-,-s7 1.561 imam-31cm UnrmosnrasPAr Nrs 1/1966 Cerveny 3241153 uorneknersaertces 1 1nj i;"1z.A.; Arm-1m TesterFor TheExperimental am" February 1958; ELECTRONICS INDUSTRIES; pages- .i n iri ifiil il'l 325:1? a

ELECTRONICS, Automatic Measurement'Of Transistor Beta" by E. P. Hoja k Dec. 4, 1959, pages I M- 5.

Primary Examiner-Rudolph V. Rolinec Amman! Examiner--ErnestF.Karlsen filtorlrex fidyard J. Norton ABSTRACT: A method and a circuit for measuring the am- .plification t'sctor'(b'eta) of an in-circuit transistor is disclosed.

A first potential of one polarity is applied across a first fixed resistor and the collector-emitter path of the transistor. A

" second potential of opposite polarity is applied across a first vlriableiresistor ai'id the first fixed resistor, the resistance of the first variable resistor being'adjusted until the net voltage across-thefirst fixed resistor is zero. The first potential is also applied'througha second fixed resistor, a second variable re-' sistor, and the baseemitter path of the transistor, and the second variable resistor is adjusted until a predetermined current flows through the first fixed resistor and the collectorerhitter path of the transistor,- A meter is provided formeasur- I 'ing'the currentthroug'h the first and second fixed resistors and Wl'i'li'llii? "'5"- 5 T Y r positions as arrived atas explained above, the switch moving element 40 is moved to cause it to contact with the switch point 44, as shown in Figure 3 and the meter scale 70 is read to give the beta of the transistor 60 under test. This beta test is made without taking this transistor 60 out of the apparatus 62 in spite of the fact that shunt circuits for the-transistor 60 represented by the elements 63, 64 and 66 are present in the apparatus 62. The accuracy of the beta measurement will be reducedrin inverse proportion to the resistances of the shunt elements 63, 64 and 66. However, the accuracy of the beta measurement will be sufficient for many tests and for most circuit repair work.

If the transistor to be tested is not connected in a circuit, it is either inserted in the socket 52 if the transistor has pinlike terminals, or its terminals are properly contacted by the probes 54, 56 and 58. The steps taken to test for the beta of a transistor which is not in a circuit are the same as the second and third step given above. That is, the slider 34 remains on its infinite resistance point 36, since there is no shun t circuit to correct for if thetransistor to be tested is not in a circuit.

It will be noted that when the meter reads or X] on the scale 68 when the moving switch element 40 is in contact with switch point 46, and when the meter reads 1 on the scale 70 when the moving element 40 is in contact with the terminal 44, the same amount of current is flowing in the output electrode or collector to the reference electrode or emitter circuit is calibrated to give the beta of the transistor 60 for other positions of the needle 13 of the meter 12 when the switch moving element 40 is in the position shown in FIG. 3, if the position of the slider 24 had been adjusted to cause the needle 13 of the meter 12 to indicate 10 or X] on its scale 70 while the moving element 40 was in contact with the point 46. For example, for a needle 13 position of 2 on the scale 70, the current flowing in the base to emitter circuit of the transistor 60 is one half the current flowing in the collector to emitter circuit thereof.

If it is desired to test the transistor 60 with other, larger collector to emitter currents, the slider 24 is manipulated in the step illustratedby FIG. 2 to cause the needle 13 of the meter 12 to take the or X2 position on the scale 68 (or to take the position or X3 or any other position on the scale 68 as desired), and then the reading on the scale 70, when the switch moving element 40 is in the position shown in FIG. 3, is multiplied by the multiplier 2 (or 3 or whatever it may be), as had been indicated by the needle 13 of the meter 12 in the position of the switch illustrated in FIG. 2.

Variations of the measuring apparatus and method will occur'to a person skilled in the art. While the device for measuring the beta of a transistor either in or out of circuit has been disclosed, thealpha of the transistor 60 may be measured by interchanging the positions of the emitter and base of the transistor 60. While means to measure the amplification factor of an NPN transistor has been disclosed, by proper connection of the :voltage sources 14 and 50 and of the meter 12, the amplification factor of a PNP transistor may be measured. Therefore, the above description is to be taken as illustrative and not in a limitingsense.

. What-l claim is:

1. An amplification factor measuring circuit comprising a first and a second terminal for a meter,

' a first, a second and a third contact element for making contacts respectively to the output electrode, the control electrode and the reference electrode of a transistor to be tested,

a first resistor, I

a circuit from said first contact element through said first resistor to said first meter terminal,

a first variable resistor having an infinite resistance adjustment,

a second resistor,

a circuit from said second contact element through said variable resistor and said second resistor in series to said first meter terminal,

a switch having two switch points and a moveable arm which can make contact with either one of said points,

means for connecting one switch point of said switch to said first contact element,

means for connecting the other switch point of said switch to the junction of said first variable resistor and said second resistor,

means for connecting the moveable element of said switch to said second meter terminal,

a first pair of terminals for connection to a source of direct current voltage,

a circuit from said third contact element to one of said first pair of terminals,

a circuit from the other terminal of said first pair of terminals to said first meter terminal,

a second pair of terminals for connection to a source of direct current voltage,

means for connecting one terminal of said second pair of terminals to said other terminal of said first pair of terminals, said one terminal of said second pair of terminals being of opposite polarity from said other terminal of said first pair of terminals,

a second variable resistor having an 'justment, and

means for connecting the other terminal of said second pair of terminals through said second variable resistor to said first contact element.

2. The invention as expressed in claim 1 in which said second resistor has a resistance which is several times that of said first resistor.

3. The invention as expressed in claim 1 in which said infinite resistance adsecond resistor has a resistance which is several times that of i said first resistor and in which a meter is connected between said meter terminals, said meter having a scale which indicates the ratio of current flow in said circuit including said first voltage source and said third contact element, to the current flowing in the circuit of said second contact element.

4. The invention according to claim 3 wherein said meter has one needle and two scales, said first scale indicating a plurality of multiplication factors and said second scale indicating said amplification factor divided by a selected one of said multiplication factors said selected one of said multiplication factors being dependent upon the resistive value of said first variable resistor.

5. Apparatus for measuring the current amplification factor of an in-circuit transistor having an output electrode, a control electrode and areference electrode without removing the transistor from the circuit, comprising:

means, including a resistance first resistor, for applying a first voltage between said output electrode and said reference electrode and for applying a second voltage across said first resistor;

adjustable voltage means for applying a third voltage across said resistor, said third voltage having a magnitude equal to and a polarity opposite from the respective magnitude and polarity of said second voltage;

an input circuit for applying a first current to said control electrode to cause a predetermined current to flow through said resistor; and

means for measuring the ratio of said predetermined current to said first current. i

6. The invention according to claim 5 wherein said input circuit includes a second resistor and said measuring means includes a meter and means for alternately connecting the meter across said first resistor and said second resistor.

7. Theinvention according to claim 6 wherein said meter has two scales, said first scale indicating a plurality of multiplication factors and said second scale indicating the amplification factor divided by a selected one of said multiplication factors.

8. The method of measuring the amplification factor of a transistor which has an output electrode, a reference electrode and a control electrode comprising the steps of:

applying a voltage across the combination of a resistor coupled in series with the output electrode and reference electrode of said transistor to cause a first current of one polarity to flow through said resistor;

causing a second current equal in magnitude to and opposite in polarity from said first current to flow through said resistor;

causing a third current to flow between said control electrode and said reference electrode without varying said second current to cause a predetermined current to flow through said resistor; and

measuring the ratio of said predetermined current and said third current.

9. The method of measuring the amplification factor of a transistor having an output electrode, a control electrode and a reference electrode when in a circuit and without removing said transistor from said circuit comprising the steps of:

applying a first voltage across a first circuit including a first resistor in series with said output electrode and said reference electrode while leaving a second circuit open, said second circuit including said control electrode and said reference electrode, whereby a first current flows through said first resistor; applying a second voltage which is variable across said first resistor and varying said second voltage until said first current is negligible; applying a third voltage which is variable across said control electrode and said reference electrode and varying said third voltage until a predetermined current flows through said first resistance, whereby a second current flows through said second circuit; and

obtaining the ratio of said predetermined current to said second current.

10. The invention according to claim 9 wherein said first voltage is obtained from a direct current voltage source and said second and third voltages are obtained from direct current voltage sources in series with variable resistances, said second and third voltages being varied by varying said variable resistances. 

1. An amplification factor measuring circuit comprising a first and a second terminal for a meter, a first, a second and a third contact element for making contacts respectively to the output electrode, the control electrode and the reference electrode of a transistor to be tested, a first resistor, a circuit from said first contact element through said first resistor to said first meter terminal, a first variable resistor having an infinite resistance adjustment, a second resistor, a circuit from said second contact element through said variable resistor and said second resistor in series to said first meter terminal, a switch having two switch points and a moveable arm which can make contact with either one of said points, means for connecting one switch point of said switch to said first contact element, means for connecting the other switch point of said switch to the junction of said first variable resistor and said second resistor, means for connecting the moveable element of said switch to said second meter terminal, a first pair of terminals for connection to a source of direct current voltage, a circuit from said third contact element to one of said first pair of terminals, a circuit from the other terminal of said first pair of terminals to said first meter terminal, a second pair of terminals for connection to a source of direct current voltage, means for connecting one terminal of said second pair of terminals to said other terminal of said first pair of terminals, said one terminal of said second pair of terminals being of opposite polarity from said other terminal of said first pair of terminals, a second variable resistor having an infinite resistance adjustment, and means for connecting the other terminal of said second pair of terminals through said second variable resistor to said first contact element.
 2. The invention as expressed in claim 1 in which said second resistor has a resistance which is several times that of said first resistor.
 3. The invention as expressed in claim 1 in which said second resistor has a resistance which is several times that of said fiRst resistor and in which a meter is connected between said meter terminals, said meter having a scale which indicates the ratio of current flow in said circuit including said first voltage source and said third contact element, to the current flowing in the circuit of said second contact element.
 4. The invention according to claim 3 wherein said meter has one needle and two scales, said first scale indicating a plurality of multiplication factors and said second scale indicating said amplification factor divided by a selected one of said multiplication factors said selected one of said multiplication factors being dependent upon the resistive value of said first variable resistor.
 5. Apparatus for measuring the current amplification factor of an in-circuit transistor having an output electrode, a control electrode and a reference electrode without removing the transistor from the circuit, comprising: means, including a first resistor, for applying a first voltage between said output electrode and said reference electrode and for applying a second voltage across said first resistor; adjustable voltage means for applying a third voltage across said resistor, said third voltage having a magnitude equal to and a polarity opposite from the respective magnitude and polarity of said second voltage; an input circuit for applying a first current to said control electrode to cause a predetermined current to flow through said resistor; and means for measuring the ratio of said predetermined current to said first current.
 6. The invention according to claim 5 wherein said input circuit includes a second resistor and said measuring means includes a meter and means for alternately connecting the meter across said first resistor and said second resistor.
 7. The invention according to claim 6 wherein said meter has two scales, said first scale indicating a plurality of multiplication factors and said second scale indicating the amplification factor divided by a selected one of said multiplication factors.
 8. The method of measuring the amplification factor of a transistor which has an output electrode, a reference electrode and a control electrode comprising the steps of: applying a voltage across the combination of a resistor coupled in series with the output electrode and reference electrode of said transistor to cause a first current of one polarity to flow through said resistor; causing a second current equal in magnitude to and opposite in polarity from said first current to flow through said resistor; causing a third current to flow between said control electrode and said reference electrode without varying said second current to cause a predetermined current to flow through said resistor; and measuring the ratio of said predetermined current and said third current.
 9. The method of measuring the amplification factor of a transistor having an output electrode, a control electrode and a reference electrode when in a circuit and without removing said transistor from said circuit comprising the steps of: applying a first voltage across a first circuit including a first resistor in series with said output electrode and said reference electrode while leaving a second circuit open, said second circuit including said control electrode and said reference electrode, whereby a first current flows through said first resistor; applying a second voltage which is variable across said first resistor and varying said second voltage until said first current is negligible; applying a third voltage which is variable across said control electrode and said reference electrode and varying said third voltage until a predetermined current flows through said first resistance, whereby a second current flows through said second circuit; and obtaining the ratio of said predetermined current to said second current.
 10. The invention according to claim 9 wherein said first voltage is obtained from a direct curreNt voltage source and said second and third voltages are obtained from direct current voltage sources in series with variable resistances, said second and third voltages being varied by varying said variable resistances. 